> Why does such a tool need an API and an external connection?
So time spent on different devices can be tracked under a single user account, I guess.
This problem exists indeed and I encounter it from time to time when I switch between desktop and laptop. My time tracking tool [0] is local-only and I still didn't come up with a solution that lets it remain so and a PWA at the same time. Solutions that allow you to sync data without a dedicated server (as in running specifically for your app needs) range from trivial ones like storing the data in a Google Drive all the way to P2P.
Ideally a tool like this should be a desktop app. But people tend to use multiple devices or even change their devices and then the question of data migration comes in.
It also helps to be able to access these stats anywhere instead of just on the device it is installed on.
Eventually, this can become a hybrid. But the expedient solution is what we have now.